The invention relates to a cyclone separator provided with a tube with an axial inflow opening and an axial outflow opening, a stationary swirl body arranged in the tube, designed for imparting a spiraling movement to an axially directed gas/liquid flow entering the tube, in use, while in the case wall of the tube a slot is provided for discharging from the inner space of the tube liquid in the gas/liquid flow that has been slung radially outwards under the influence of the centrifugal force prevailing in the spiraling flow.
Such a cyclone separator is known from, for instance, NL-C-1016114. In that publication, but also in other publications, the cyclone separator is provided with several slots running in axial direction. Further, the known cyclone is provided with a secondary gas inflow opening provided in the tube case wall, located upstream of the swirl body, which opening is connected via a secondary gas pipe to a chamber in a core of the swirl body, which chamber is provided with a number of secondary gas outflow openings which are preferably located between swirl blades provided on the core of the swirl body. The secondary gas inflow opening and secondary gas outflow openings result in a secondary gas flow which egresses from the tube via the slots and, via the secondary gas inflow opening, the secondary gas duct, the chamber and the secondary gas outflow openings, ends up in the tube again. The purpose of the secondary gas flow is to promote the entrainment of liquid through the slots.
In practice, it appears that not the same amount of secondary gas flows through each slot. As a consequence, the liquid separation varies per slot Moreover, the amount of through-flowing secondary gas per slot varies in time, so that an unstable separation behavior occurs, which is undesired. The quality of the known cyclone separators is determined by the separating efficiency of the least optimally functioning slot of the cyclone separator.
The invention contemplates a cyclone separator without the drawbacks mentioned hereinabove and to that end provides, according to the invention, a cyclone separator of the type described in the opening paragraph, which is characterized in that only one slot is provided, while the slot runs in a spiral-shaped path over the case wall of the tube.
So-called CFD-studies (computer fluid dynamics) as well as experiments in practice have shown that with one spiral-shaped slot a much higher separating efficiency is obtained. Moreover, variation in separating efficiency in time does not occur any longer. As only one spiraling slot is involved, the inner surface of the tube forms an outstanding coalescence surface on which the liquid droplets present in the gas flow precipitate and accumulate to form a liquid film. This liquid film is entrained by the spiraling gas flow to the spiral-shaped slot to exit there. As there is only one slot, in the slot a considerably higher gas outflow velocity prevails than with several slots, so that the liquid is pulled loose from the slot better by the gas flowing through the slot. Thus, a very high separating efficiency is effected.
An optimal separating efficiency is obtained when, according to a further embodiment of the invention, the spiral of the slot rotates clockwise around the central axis of the tube, while, in use, the spiraling gas flow in the tube rotates counter-clockwise around the central axis of the tube, or vice versa.
As a result of the opposite direction of pitch of the slot and of the spiraling flow, the separating efficiency is even more increased. From various CFD-studies it appears that an optimal separation is obtained when, according to a further embodiment of the invention, the spiral-shaped slot extends over substantially 180 degrees around the tube surface, while the pitch angle is preferably in the range of 30-60 degrees, more in particular is approximately 45 degrees.
When no means are present for discharging gas having egressed via the slot, the gas having egressed via the slots will eventually reenter the tube via the slot. The fact is that the tubes of the cyclone separators are connected by their ends to the walls of so-called liquid collecting boxes which, apart from a discharge for liquid, are otherwise closed. Therefore, in such a liquid collecting box, a certain excess pressure will start to prevail, as a result of which the gas having egressed via the slot will tend to reenter the tube via that same slot. This may present a certain danger to the entry of liquid via the slot, which is highly undesired because the very purpose of the cyclone separator is to separate liquid from the gas/liquid flow flowing through the tube. This phenomenon, for that matter, also presents itself in the known cyclones with several axial slots.